Found on news://news.aioe.org/comp.mobile.android
Note: I'm fully aware that hiding the SSID broadcast is not for security
reasons, but many people do not realize hiding it is for privacy reasons!
Specifically, most Android phones driving by your home will upload your GPS
location and your unique router BSSID even if you have "_nomap" appended to
the SSID (unique because you want your unique-as-possible SSID to stay out
of voluminous Internet butterfly/hash tables but that's a separate thing).
Even if Google/Mozilla respect the _nomap on the server side... notice that
distinction because it's the whole point that it's already uploaded even
if you have "_nomap" appended (where we can forget nowadays about
optout)... there's no guarantee that the others (e.g., Kismet, Wiggle,
etc.) will respect the _nomap optout request).
The solution is to prevent "most" Android phones from even seeing your
SSID, which can only be done by hiding the broadcast - where - if someone
knows what they're doing, of course they will see your (hidden) SSID -
but "most" phones will not upload a hidden ID to the Internet servers,
and that's why you hide it.
Of course, once you hide it, then you have to worry about your phone
constantly trying to reconnect to it (which shouts out your supposedly
unique SSID everywhere you go), so you also need to turn off the
auto-reconnection option in Android - which is very easily done.